1. Field of the Invention
The present invention relates to a liquid discharge head for discharging a liquid droplet such as an ink droplet and performing recording on a recording medium, and in particular, to the liquid discharge head for performing ink jet recording.
2. Related Background Art
An ink jet recording system is one of so-called non-impact recording systems. As for the ink jet recording system, noise generated on recording is almost negligible and high speed recording is possible. The ink jet recording system is capable of recording on various recording media and fixing ink on so-called standard paper without requiring a special process, and in addition, it allows a high-definition image to be obtained at a low price. Because of these advantages, the ink jet recording system is rapidly becoming widespread in recent years not only for a printer as a peripheral of a computer but also as a means of recording of a copying machine, a facsimile, a word processor and so on.
Ink discharge methods of the generally used ink jet recording system include a method of using an electrothermal converting element such as a heater as a discharge energy generating element used for discharging ink droplets and a method of using a piezoelectric element such as a piezo element as the same. Either method can control the discharge of the ink droplets by means of an electrical signal. According to a principle of the ink discharge method using the electrothermal converting element, a voltage is applied to the electrothermal converting element to instantaneously heat the ink in the proximity thereof so as to discharge the ink droplets at high speed by means of an abrupt bubbling pressure generated by phase change of the ink on boiling. On the other hand, according to the principle of the ink discharge method using the piezoelectric element, the voltage is applied to the piezoelectric element to displace it so as to discharge the ink droplets by means of the pressure generated on the displacement.
The ink discharge method using the electrothermal converting element has advantages such as no need to secure large space for placing the discharge energy generating element, a simple structure of a record head and easy integration of nozzles. On the other hand, the problems unique to this ink discharge method include change in volume of a flying ink droplets due to thermal storage of the heat generated by the electrothermal converting element and so on in the record head, an adverse effect caused on the electrothermal converting element by cavitation due to disappearance of bubble, and the adverse effect caused on a discharge characteristic of the ink droplets and image quality by the air melted into the ink becoming remaining bubbles in the record head.
As for the methods of solving these problems, there are the ink jet recording systems and record heads disclosed by Japanese Patent Application Laid-Open No. 54-161935, Japanese Patent Application Laid-Open No. 61-185455, Japanese Patent Application Laid-Open No. 61-249768 and Japanese Patent Application Laid-Open No. 4-10941. To be more specific, the ink jet recording systems disclosed by the above patents laid-open have a structure wherein the electrothermal converting element is driven by a recording signal and the bubbles thereby generated are aerated to the outside air. It is possible, by adopting the ink jet recording systems, to stabilize the volume of the flying ink droplets and discharge a minute amount of the ink droplets at high speed. And it becomes possible, by resolving the cavitation generated on disappearance of the bubbles, to improve durability of the heater so as to easily obtain a further high-definition image. As for the structure for having the bubbles communicate with the outside air in the above patents laid-open, there is a named structure for significantly reducing the shortest distance between the electrothermal converting element for generating the bubbles in the ink and a discharge port which is an opening for discharging the ink compared to the past.
The structure of the record head of this type will be described hereafter. It has an element substrate on which the electrothermal converting element for discharging the ink is provided and a flow path composition substrate (also referred to as a discharge port substrate) joined with the element substrate to constitute flow paths of the ink. The flow path composition substrate has a plurality of nozzles through which the ink flows, a supply chamber for supplying the ink to each of the nozzles, and a plurality of discharge ports which are nozzle end openings for discharging the ink droplets. The nozzle is comprised of a bubbling chamber in which bubbles are generated by the electrothermal converting element and a supply path for supplying the ink to the bubbling chamber. The element substrate has the electrothermal converting element provided to be located in the bubbling chamber. The element substrate also has a supply port provided for supplying the ink to the supply chamber from the rear surface on the opposite side of the principal surface in contact with the flow path composition substrate. And the flow path composition substrate has the discharge ports provided at positions opposed to the electrothermal converting elements on the element substrate.
As for the record head constituted as above, the ink supplied from the supply port into the supply chamber is provided along each nozzle so as to be filled in the bubbling chamber. The ink filled in the bubbling chamber is caused to fly by the bubbles generated due to film boiling by the electrothermal converting element in the direction almost orthogonal to the principal surface of the element substrate so that it is discharged as the ink droplets from the discharge ports.